Generally, the sound generated by the mills is the parameter used to estimate the proper operation of the mills, since it is a highly complex process to implement.
Over the years, different instruments and computer systems have been commonly used for sound analysis in a wide variety of processes such as cement production, plastic bottle fabrication, food conservation, and mineral processing. The latter field still reveals deficiencies despite the current existence of products for monitoring the condition of this equipment, thus culminating in large fields of study and development that could potentially increase process efficiency.
Specifically, grinding is a technique used to grind metals or non-metallic minerals, a process that is present in mining plants. The grinding process allows for the reduction of the size of the mineral up to having the final desired size through several items that work through impact, crushing or wear. There are several types of mills, such as ball mills, bar mills, FAG (autogenous) mills and SAG (semi-autogenous) mills. Most of the mills operate under the same principle, which consists of elevating the material within a cylindrical mill up to the point that they fall again to the bottom of the mill. The elevation of the load (mineral to grind, balls to carry out the grinding, and water) is performed by the rotation of the mill, making use of equipment that transports the material called 1the inner lining. The combined action of impacts, falls, slippage, and crushing of the ore reduce the size of the particles as they advance through the mill.
Currently, there are grinding systems that have certain disadvantages that limit efficiency. The inside of mills have a short life span due to the level of impact it receives, which lends itself to the mill being used less frequently as a result of stoppages in production and for repairs and increases the cost of the mineral grinding line. Thus, some systems have been developed to obtain information from the mill.
Due to the difficulties in instrumenting a mill so as to understand its internal operation, the sound emitted becomes a key parameter. Currently, the device called “Electric Ear” is one of the most used instruments. This device estimates the volume of the mill occupied by the mineral, grinding means, and/or water, comprised of a microphone that detects the intensity of the noise close to the mill, without distinguishing whether the origin of the noise was caused by the movement of the mill or by an external cause independent of the grinding process. It has an exit electrical signal for the control system. Only the operator is in charge of keeping a proper noise level, since the instrument does not carry out any other analysis that provides information about the internal operation of the mill.
The sound analysis system currently used in mills, captures and analyzes sound signals in real-time by a centralized system, which also processes sound and communicates with the control system by means of the OPC (Object Linking and Embedding for Process Control).
Currently, systems use servers with special hardware features designed to execute advanced analysis algorithms; these require large memory space, high speed, etc. The system communicates with databases to save and analyze data and transfer it to the control systems.
The following patents serve as a background. This is the case of the descriptive report for the Spanish Patent with Publication No. ES8704759 and priority number ZA19850003617 19850514, which describes a procedure and device to monitor the load level in the mills, which include: a) detecting the prevailing sound level in two positions, b) generating signals that depend on the sound level of two positions, c) comparing the sound levels signals, and d) generating a control signal to regulate the load feeding regime to the mill. It consists of the following: two sound level detectors of the impact located between both detectors, a signal gauge of the detectors that generates a control signal, a visual representation that indicates the point of impact, and a control module that increases the mineral feeding regime.
In the descriptive report of the United States Patent with Publication Number US20040255679 and priority number 190-2003 31.01.2003 CL, an instrument that uses four to eight sound detectors, unites with industrial data acquisition and a processing system based on computers where virtual instrumentation software is executed. The types of impact that occurred are detected and classified, a record is created, and mill operation risk is determined. This is shown to the operator on a display, through graphs of each microphone.
The descriptive report of the Canadian Patent with Publication Number CA2456608 and priority number 189-203 31.01.2003 CL is very similar, where a system and method of direct, dynamic, and online measurement of different parameters are described, which are related to the volume occupied by the internal dynamic load of tube mills when the mill is in operation. More specifically, an online measurement of the total filling of volumetric dynamic load, volumetric dynamic of the balls load, and the apparent density of the mill internal load are undertaken. This includes a series of wireless acoustic sensors connected to the external body of the mill, a receptor and/or conditioning units located close to the mill, a processing unit, and a communication unit.
Despite the advancement and sophistication that these technologies represent, there are some associated disadvantages. First, current systems used to analyze the sound in the mills are instruments that process the signals in an analog manner, using components such as operation amplifiers, thus a deep analysis of the signal is not performed, yet the system is imitated in order to make comparisons of intensity.
In turn, current systems are, in reality, a software solution, thus the performance in terms of response time and reliability are not optimal. Second, these require diverse components to function such as servers, storage, cameras, and data communication that collectively deliver results to the control system. Using servers and diverse components make these systems more costly and difficult to use; additionally, they require more maintenance. Both the software and hardware of a server are generally determinant elements; specific software and hardware is necessary to meet application needs. In a server, if the numbers of users at any given time were high, the server would stop responding to the users thus, without being able to know that the system failed, communication with the control would be incorrect.
Industrial quality OPCs demand complex configuration procedures, making them not feasible for plant personnel; therefore, to use OPCs, hours of engineering and maintenance from qualified personnel are required in order to establish a proper and efficient use in the design and administration of databases. The implementation can be costly, regarding both the physical equipment (servers, memory, installations, etc.) and the logical equipment (operating systems, software, etc.). In addition to the database acquisition and maintenance cost, the equipment requires a high volume hard disk and sufficient RAM capacity to work properly. In the event that the database becomes corrupted, the recovery process is much more complex to implement. The fact that everything is centralized makes the system more vulnerable to potential failure, thus it is necessary to make security copies regularly
The system requires high bandwidth since it transfers images to the server in order to analyze them while not interrupting data flow at the information level.
Finally, the systems that perform the sound processing techniques are computer systems with software for image analysis at the information network level; that is to say, there is no direct communication with the control system in addition to not being deterministic systems.
Therefore, an area of opportunity related to current technologies consists of a system that analyses the sound and reduces the complexity and cost of current equipment, without affecting the efficiency and precision required to carry out the analysis which in turn can be compact and robust equipment. For example, an embedded vision system that works at the controller level may be used, this way the use of servers and components that make the system costly and complex would not be required, allowing the facility to be part of a control system such as a remote node controlled by a master controller.